Carbide- and boride-based ultrahigh temperature ceramics (UHTCs) are the materials of choice for hypersonic vehicles and scramjet engines. Nevertheless, these UHTCs are prone to oxidation in an oxygen-containing atmosphere. In addition, the high density of these UHTCs limits their widespread applications in the aerospace industry. To address the urgent need for lightweight thermal protection materials (TPMs) and mitigate oxidation-induced volume changes, a novel HfO₂–SiBOC ceramic was designed in this work, in which amorphous SiBOC is the matrix, while nanosized HfO₂ acts as the reinforcement phase. The advantages of these HfO₂–SiBOC ceramics are as follows. This HfO₂–SiBOC ceramic simultaneously achieves light weight by tuning the SiBOC matrix content and mitigates oxidation through nanosized HfO₂ uniformly dispersed in the matrix via preferential oxidation of Hf from the precursor. To achieve the above goals, a novel amber liquid SiHfBOC precursor was synthesized via a sol–gel and solvothermal method as the first step. The precursor, featuring Si–O–Si, Si–O–B main chains and Si–O–Hf side chains, achieves a high ceramic yield of 80.8 wt%. Its polymerization mechanism and properties were studied. The effects of the Hf/Si ratio and pyrolysis temperature on the SiHfBOC ceramic powder composition, microstructure evolution behavior, and oxidation resistance were systematically investigated. Based on the above results, HfO₂–SiBOC bulk ceramics were then prepared by hot pressing sintered powders. Oxyacetylene flame ablation tests at 2000 °C for 300 s confirmed their near-nonablation behavior, demonstrating exceptional ablation resistance. The ablation mechanism is elucidated. This work provides a new strategy for designing lightweight high-performance polymer-derived ceramics (PDCs) for ultrahigh temperature applications.

To meet the stringent demands for toughening and ablation resistance in high-speed aircraft components, C/C-SiHfCB composites were fabricated by introducing a novel liquid SiHfCB precursor into a porous C/C matrix via high-pressure precursor infiltration and pyrolysis. This approach yielded an integrated three-dimensional continuous ceramic phase tightly bonded to the matrix. The composite achieved a flexural strength of 237 ± 42 MPa with non-brittle fracture, a critical thermal shock temperature difference of 912℃. During oxyacetylene flame tests, extremely low linear ablation rates of 5.7 × 10⁻⁴ mm/s and 15.6 × 10⁻⁴ mm/s were recorded at 2000℃ and 2150℃, respectively. An effective oxygen diffusion barrier consisting of an HfO₂ skeleton with SiO₂-filled pores was formed. This study offers a viable strategy for the synergistic optimization of mechanical and ablation properties.